1. Field of the Invention
The present invention relates to directional antennas and particularly to a short backfire antenna having both sum and error radiation patterns in the H-plane.
2. Description of the Prior Art
The presently known short backfire antenna utilizes a shallow rimmed pan-type reflector and a smaller planar reflector plate or disc spaced apart about one-half wavelength along a common axis to form a resonant cavity therebetween. A single dipole feed element is positioned along the axis between the planar reflectors to provide a highly directive endfire type pattern in the H-plane. Such an antenna is described more fully in U.S. Pat. No. 3,508,278 issued Apr. 21, 1970. This antenna is capable of providing a single lobe unidirectional or sum pattern in the E- and H-planes. It does not, however, provide an error, or split lobe pattern, having a broadside null in the H-plane, which is desirable in some particular target direction finding and interrogation applications. In order to obtain such a combination of sum and error patterns in the past, it was necessary to use more complex broadside arrays of nine or more dipoles.